WATER 437 



The Coli-Typhoid Group. 



i. Number nine tubes of bile salt broth (vide page 

 1 80), consecutively from i to 9. 



2. To No i add i c.c. 



2 add 2 c.c. 



3 add 5 c.c. 



of the original water sample 

 before the filtration is com- 

 menced. 



3. To the remaining tubes of bile salt broth add 

 varying quantities of the suspension by means of 

 suitably graduated sterile pipettes, as follows : 



No. 4 . . . 0.05 c.c. (equivalent to 10 c.c. of the original water sample). 



No. 5 . . . 0.125 c.c. (equivalent to 25 c.c. of the original water sample). 



No. 6 . . .0.25 c.c. (equivalent to 50 c.c. of the original water sample). 



No. 7 . . .0.5 c.c. (equivalent to 100 c.c. of the original water sample). 



No. 8 . . . i .o c.c. (equivalent to 200 c.c. of the original water sample). 



No. 9 ... 2.5 c.c. (equivalent to 500 c.c. of the original water sample). 



4. Put up each tube anaerobically in a Buchner's 

 tube and incubate at 42 C. 



5. The subsequent steps are identical with those 

 described under the Enrichment method (see page 428 

 to 431; Steps 8 to 1 8) . 



Alternative Methods. 



A few of the older methods for the isolation of the members of 

 the coli-typhoid groups are refered to but they are distinctly 

 inferior to those already described. 



(A) The Carbolic Method : 



1. Take ten tubes of carbolised bouillon (vide page 202) and 

 number them consecutively from i to 10. 



2. Inoculate each tube with a different amount of the water 

 sample or suspension, as in the previous method. 



3. Incubate aerobically at 37 C. 



4. Examine the culture tubes after twenty-four hours' 

 incubation. 



5. From those tubes which shows signs of growth, pour plates 

 in the usual manner, using carbolised gelatine (vide page 202) in 

 place of the ordinary gelatine, and incubate at 20 C. for three, 

 four, or five days as may be necessary. 



6. Subucltivate from any colonies that make their appearance, 

 and determine their identity on the lines laid down in the previous 

 method. 



(B) Parietti's Method: 



i. Take nine tubes of Parietti's bouillon (vide page 202) 

 i. e., three each of those containing o. i c.c., 0.2 c.c., and 0.5 c.c. 



